This application is based on application No. 99-55895 filed in the Korean Industrial Property Office on Dec. 8, 1999, the content of which is incorporated hereinto by reference.
(a) Field of the Invention
The present invention relates to a negative active material slurry composition for a rechargeable lithium battery and a method of manufacturing a negative electrode using the same, and more particularly, to a negative active material slurry for a rechargeable lithium slurry composition exhibiting good cycle life characteristics.
(b) Description of the Related Art
Carbonaceous material used as a negative active material for a rechargeable lithium battery are classified into amorphous carbon and crystalline graphite according to the crystallinity of the substance. Crystalline graphite includes artificial graphite and natural graphite. Typical examples of artificial graphite may include mesocarbon fiber (MCF) and mesocarbonmicro beads (MCMB). They are generally used in rechargeable lithium batteries.
The high crystallinity of natural graphite results in good initial discharge capacity, but flake type configuration materials are produced during the pulverizing step, and these flakes cause an irreversible-capacity increase at the edge of the natural graphite. In addition, natural graphite is severely compressed during electrode preparation so that it becomes difficult to absorb an electrolyte into natural graphite, and the lithium ion transferring route is longer than with artificial graphite. Accordingly, natural graphite exhibits inferior cycle life characteristics, particularly high-rate cycle life characteristics, as compared to artificial graphite of globular, fibrous or random configurations.
Japanese Patent Laid-Open No. Hei 11-40150 discloses a method producing a boron-based oxides negative electrode. The boron-based oxide negative electrode exhibits twice the cycle life characteristics of an a SnO metal oxide negative electrode. However, the boron-based oxides such as B2O3 are glassy and very brittle such that it is difficult to produce a negative electrode using them.
Japanese Patent No. Laid-Open No. Hei. 9-161776 discloses that metal powder such as Cu, Ni or Fe is added to an active material to increase conductivity between the active material particles, and the metal particles have a diameter one-twentieth to one-fifth that of the active material particle size. A battery using the resulting material exhibits improved cycle life characteristics. Furthermore, Japanese Patent Laid-Open No. Hei 9-245798 discloses that metal particles with a diameter of 2 xcexcm or less is added to an active material to increase conductivity between the active material, thereby improving cycle life characteristics. However, conducting agents such as Cu, Ni or Fe with a one-twentieth to one-fifth diameter of the active material particles and a conducting agent with a diameter of 2 xcexcm or less are very expensive. Furthermore, the heavy conducting agent powder tends to separate from the light active material and the conducting agent is precipitated.
Various patents such as Japanese Patent Laid-Open Nos. Hei. 8-45499 and Hei. 8-69797 disclose that copper oxide or silicate is coated on a surface of the graphite active material in the form of small islands using electroless plating to increase conductivity between the active materials. However, this method requires a high cost and additional steps for producing oxides.
It is an object of the present invention to provide a negative active material slurry composition for a rechargeable lithium battery which can improve cycle life characteristics.
It is another object to provide a method of manufacturing a negative electrode for a rechargeable lithium battery using the active material slurry composition.
These and other objects may be achieved by a negative active material slurry composition for a rechargeable lithium battery. The negative active material slurry composition includes a negative active material, a compound and an organic solvent. The compound includes elements selected from transition metals, alkaline metals, alkaline earth metals or semi-metals.
In order to achieve these objects and others, the present invention provides a method of manufacturing a negative electrode for a rechargeable lithium battery. In this method, a negative active material is mixed with a compound that includes elements selected from transition metals, alkaline metals, alkaline earth metals or semi-metals. The mixture is added to an organic solvent to prepare a negative active material slurry composition, and the resulting product is coated on a current collector. The coated current collector is dried and the dried current collector is pressed.